JPH0955532A - Semiconductor light receiving element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light receiving element wherein thinning and cost reduction can be realized at the same time, when the element is employed for an optical pickup of a photo-electro-magnetic disc recording reproducing equipment. SOLUTION: On a semiinsulating semiconductor substrate 1, an N-type semiconductor layer 2 is formed, on which a pair of comb type electrodes 3, 4 are formed in such a manner that they face each other and are brought into Schottky contact with the N-type semiconductor layer 2. The comb type electrodes 3, 4 are designed to operate as wire grid polarizers at the time of operating, the comb type electrode 4 is, e.g. grounded, and a bias voltage VD is applied to the comb type electrode 3. A light entering a light receiving surface is polarized and isolated by the comb type electrodes 3, 4. One polarized light passes gaps of comb type electrodes 3, 4, enters the N-type semiconductor layer 2, and is detected. The other polarized light is reflected by the light receiving surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element, and more particularly to a so-called comb-shaped electrode facing type semiconductor light receiving element.

[0002]

2. Description of the Related Art In recent years, recording / reproducing devices for magneto-optical disks have been commercialized. Among the magneto-optical disk recording / reproducing devices, particularly in the portable type, it is important to reduce the thickness and cost of the optical pickup for reproducing the magneto-optical disk.

By the way, in such an optical pickup for reproducing a magneto-optical disk, a polarizer is used to perform polarization separation of laser light. Conventionally, a Wollaston prism is often used as the polarizer.
However, since this Wollaston prism is expensive, it is difficult to meet the demand for cost reduction of the optical pickup.

On the other hand, for example, in a portable type compact disc player, there is a type using an optical pickup called a laser coupler. This laser coupler is a photodiode IC chip on which a laser chip, a microprism, and the like are mounted, and has a feature that it can be made thin.

Therefore, as an optical pickup of a magneto-optical disk recording / reproducing apparatus, the above-mentioned laser coupler is used as LiNbO.
The adoption of an optical pickup in which an anisotropic crystal such as ₃ (LN) crystal or KTP crystal or a polarization separation film having a multilayer structure is incorporated as a polarizer is under study.

[0006]

However, the above-mentioned optical pickup incorporating an anisotropic crystal or a polarization separation film as a polarizer has both advantages and disadvantages when the manufacturing process is taken into consideration. Nothing at the same time can satisfy the requirements for thinning and low cost of the pickup.

Therefore, an object of the present invention is to have a polarization separation function and a polarization detection function, be thin and low in cost,
It is an object of the present invention to provide a semiconductor light receiving element which can simultaneously satisfy the requirements for thinning and cost reduction of an optical pickup when used for an optical pickup of a magneto-optical disk recording / reproducing apparatus.

[0008]

In order to achieve the above object, the present invention provides a semiconductor light receiving element having a structure in which a pair of comb-shaped electrodes are provided on a semiconductor substrate so as to face each other. The electrode constitutes a wire grid polarizer.

In the present invention, typically, the pair of comb-shaped electrodes is in Schottky contact with the semiconductor substrate.

In one embodiment of the present invention, the semiconductor substrate has a structure in which a semiconductor layer of one conductivity type is provided on a semi-insulating semiconductor substrate, and the pair of comb-shaped electrodes are in Schottky contact with the semiconductor layer. ing. Here, the semi-insulating semiconductor substrate is, for example, a semi-insulating silicon (Si) substrate or a semi-insulating gallium arsenide (GaAs) substrate. The semiconductor layer is a Si layer, a GaAs layer, or the like.

In the present invention, as the material of the comb electrode, for example, titanium (Ti), platinum (Pt), aluminum (Al) or the like can be used.

In the semiconductor photodetector according to the present invention constructed as described above, since the pair of comb-shaped electrodes constitutes a wire grid polarizer, the light incident on the pair of comb-shaped electrodes is polarized and separated. To be done. One of the polarized lights obtained by this polarization separation enters the semiconductor substrate through the gap between the pair of comb-shaped electrodes to which a predetermined bias voltage is applied, and produces electron-hole pairs. These electrons and holes are collected at one comb-shaped electrode and the other comb-shaped electrode, respectively. Thereby, the polarized light is detected. On the other hand, the other polarized light obtained by the polarization separation is reflected on the surface of the comb electrode.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a semiconductor light receiving element according to a first embodiment of the present invention, FIG. 1 is a plan view thereof, and FIG. 2 is an enlarged sectional view taken along line II-II of FIG. .

As shown in FIGS. 1 and 2, in this semiconductor light receiving element, for example, an n-type Si layer or an n-type Si layer is formed on a semi-insulating semiconductor substrate 1 such as a semi-insulating Si substrate.
The type semiconductor layer 2 is provided. A pair of comb-shaped electrodes 3 and 4 are provided on the n-type semiconductor layer 2 so as to face each other and make Schottky contact with the n-type semiconductor layer 2. In this case, the comb electrodes 3 and 4 are formed of the same material as each other, for example, a metal such as Ti, Pt, or Al. Reference numerals 3a and 4a denote pad portions provided at one ends of the comb electrodes 3 and 4, respectively.

In the first embodiment, the pair of comb electrodes 3 and 4 constitutes a wire grid polarizer. In other words, these comb-shaped electrodes 3 and 4 function as a wire grid polarizer and can separate polarized light, so that the height h, the width w, and the spacing of the comb-shaped electrodes 3 and 4 can be separated according to the wavelength and incident angle of the received light. d etc. are designed.

An example of the design of the comb electrodes 3 and 4 is as follows. That is, if the received light is incident on the light receiving surface of the semiconductor light receiving element at an incident angle of 20 °, h = 0.5 μm, d = 0.7 μm, w = 0.3 μm
It is. These values of h, d, and w are optimum values for an incident angle of 20 °. At this time, the aperture ratio (w / (d + w)) of the light receiving portion of this semiconductor light receiving element is 70%.

Further, in order to obtain sufficient light receiving efficiency for the received light, a depletion layer spreading in the n-type semiconductor layer 2 at the contact portion of the comb-shaped electrode 3 to which a bias voltage V _D is applied as described later. The width W of 5 (see FIG. 2) is equal to or greater than the penetration length of the received light into the n-type semiconductor layer 2 (equal to 1 / α ₀ when the absorption coefficient of the n-type semiconductor layer 2 is α ₀ ). Is desirable.

By the way, the width W of the depletion layer 5 is expressed by the following equation.

W = [(2ε / qN _D ) (V _D + V _b )] ^1/2 (1) where ε is the dielectric constant of the n-type semiconductor layer 2 and N _D is the donor concentration of the n-type semiconductor layer 2. , Q is an elementary charge, V _D is a bias voltage, and V _b is a built-in voltage.

Therefore, the width W of the depletion layer 5 is set to n as described above.
In order to make the permeation length (1 / α ₀ ) of the received light into the n-type semiconductor layer 2 equal to or longer than that, it is necessary to set the donor concentration N _D of the n-type semiconductor layer 2 to a value obtained from the equation (1). I understand that it is good.

For example, if the n-type semiconductor layer 2 is an n-type Si layer and receives light with a wavelength of 780 nm, the penetration length 1 / α ₀ of this light with a wavelength of 780 nm into Si is about 9.
Since it is 0 μm, in order to obtain sufficient light receiving efficiency, W
Needs to be about 10 μm. In this case, assuming that the bias voltage V _D is 3 V, the n-type semiconductor layer 2 is calculated from the equation (1).
Has a donor concentration N _D of about 1 × 10 ¹⁴ cm ⁻³ .

Next, the operation of the semiconductor light receiving element according to the first embodiment configured as described above will be described.

During operation of the semiconductor light receiving element according to the first embodiment, for example, one of the comb electrodes 4 is grounded,
A bias voltage V _D is applied to the other comb-shaped electrode 3. When light is incident on the light-receiving surface of this semiconductor light-receiving element in this state, the incident light is polarized and separated by the comb-shaped electrodes 3 and 4 which constitute the wire grid polarizer. The s-polarized light obtained by this polarization separation enters the n-type semiconductor layer 2 through the gap between the comb-shaped electrodes 3 and 4, and generates electron-hole pairs.
These electrons and holes are generated by the comb electrodes 3 and 4, respectively.
Collected in. Then, polarization detection is performed by detecting the current (photocurrent) flowing between the comb electrodes 3 and 4 by this. On the other hand, the p-polarized light obtained by the polarization separation is reflected by the light receiving surface.

As shown in FIG. 3, the output terminals (comb-shaped electrodes 3 and 4) of the semiconductor light receiving element 10 according to the first embodiment are normally connected to the amplifier circuit 20, and the semiconductor light receiving element 10 of this semiconductor light receiving element 10 is connected. The output current is amplified by the amplifier circuit 20.

Next, a method for manufacturing the semiconductor light receiving element according to the first embodiment configured as described above will be described.

As shown in FIGS. 1 and 2, first, the n-type semiconductor layer 2 is formed on the semi-insulating semiconductor substrate 1. The n-type semiconductor layer 2 may be formed, for example, by doping the surface of the semi-insulating semiconductor substrate 1 with an n-type impurity by an ion implantation method or a thermal diffusion method. It may also be formed by performing epitaxial growth. When the n-type semiconductor layer 2 is formed by doping the semi-insulating semiconductor substrate 1 with an n-type impurity as in the former case, when the semi-insulating semiconductor substrate 1 is made of Si,
As the n-type impurity, for example, phosphorus (P) or arsenic (As)
Etc. can be used.

Next, after forming a resist pattern (not shown) having an opening at a portion corresponding to the comb electrodes 3 and 4 on the n-type semiconductor layer 2 by, for example, an electron beam lithography method, for example, a vacuum evaporation method. Then, a material for forming a comb-shaped electrode, for example, a metal such as Ti, Pt, or Al is deposited on the entire surface by, and then the resist pattern is removed together with the metal deposited thereon (lift-off). As a result, the comb electrodes 3 and 4 are formed.

As described above, the intended semiconductor light receiving element is manufactured.

As described above, according to the first embodiment, the pair of comb electrodes 3 and 4 provided on the n-type semiconductor layer 2 so as to face each other constitute a wire grid polarizer. As a result, a semiconductor light receiving element having a polarization separation function and a polarization detection function can be realized. Further, this semiconductor light receiving element can be made thin. Furthermore, this semiconductor light receiving element can be manufactured at low cost and stably by a semiconductor process. Therefore, when this semiconductor light receiving element is used in an optical pickup of a magneto-optical disk recording / reproducing apparatus, it is possible to simultaneously achieve a thin optical pickup and a low cost.

Next, a second embodiment of the present invention will be described. In the second embodiment, a case where a semiconductor light receiving element having a structure similar to that of the first embodiment is applied to a laser coupler used as a reproducing optical pickup of a magneto-optical disk recording / reproducing apparatus will be described.

FIG. 4 shows a laser coupler according to the second embodiment of the present invention.

As shown in FIG. 4, in this laser coupler, a pair of comb-shaped electrodes 12 forming a wire grid polarizer are provided in the light receiving portion of the photodiode IC11.
13 (only one of the comb-shaped electrodes 12 is shown in FIG. 4; see FIG. 6) are provided facing each other and in Schottky contact with the semiconductor substrate forming the photodiode IC11. Photodiode PD1 having the same structure as the semiconductor light receiving element according to the embodiment
Is configured. In addition, a photodiode PD2 formed of a pn junction is provided in the light receiving unit adjacent to the photodiode PD1. Further, the surface of this light receiving portion is coated with an antireflection film 14.
Then, a micro prism 16 having a quarter wavelength plate 15 integrally attached to the bottom surface thereof is adhered and fixed on the light receiving portion via an anti-reflection film 14 by an adhesive agent 17. On the other hand, on the photodiode IC 11, a so-called LOP (Laser on Pho) in which a semiconductor laser 19 is mounted on the photodiode 18 adjacent to the micro prism 16.
todiode) chip is mounted. Here, the photodiode 18 is for monitoring the light output from the rear end surface of the semiconductor laser 19, and thereby monitoring the light output from the front end surface.

The photodiode IC11 includes the above-mentioned photodiode PD1 and photodiode P.
In addition to D2, a current-voltage conversion amplifier for the output current signals of the photodiode PD1 and the photodiode PD2, an arithmetic processing circuit, and the like are provided.

In this case, the photodiodes PD1 and PD2 are of the four-division type, as shown in FIG.
In FIG. 5, A1 to A4 represent the photodiodes divided into four parts of the photodiode PD1, and B1 to B4 represent the photodiodes divided into four parts of the photodiode PD2.

FIG. 6 shows a quadrant photodiode PD.
An example of a specific structure of No. 1 will be shown. In FIG. 6, reference numeral 1
2a and 13a represent the pad portions of the comb electrodes 12 and 13. The distance between the comb-shaped electrodes 12 and 13 d = 0.7 μ
For m and w = 0.3 μm, the spot size of the laser beam L is, for example, numerical aperture NA = 0.45 and λ = 780 nm.
Since it is about 2.1 μm at this time, such a multi-division of the photodiode PD1 is sufficiently possible.

Next, the operation of the laser coupler according to the second embodiment constructed as described above will be explained.

As shown in FIG. 4, the laser light L emitted from the front end surface of the semiconductor laser 19 is reflected by a half mirror (not shown) on the sloped surface 16a of the micro prism 16, and then the objective lens. The light is focused by (not shown) and is incident on a magneto-optical disk (not shown) for reading a signal. The laser light L reflected by the magneto-optical disk passes through the half mirror on the slope 16 a of the micro prism 16 and enters the inside of the micro prism 16. Half (50%) of the light that has entered the microprism 16 enters the photodiode PD1 via the quarter-wave plate 15. The light that has entered the photodiode PD1 is polarized and separated by the comb electrodes 12 and 13 that form the wire grid polarizer, and the s-polarized light that is obtained by this is incident on the semiconductor substrate that forms the photodiode IC11 and is detected. It On the other hand, the p-polarized light obtained by the polarization separation is reflected by the surface of the photodiode PD1 and further reflected by the upper surface of the microprism 16 and enters the photodiode PD2 to be detected.

In this case, when the laser light L is focused on the recording surface of the magneto-optical disk, the photodiode P
The spot sizes of the laser light L on D1 and the photodiode PD2 are designed to be the same, but when the magneto-optical disk is displaced and the focal position is displaced from the recording surface, these photodiodes PD1 and PD2 are detected. The spot sizes of the upper laser light L are different from each other. Therefore, these photodiodes PD
The focus error signal can be detected by correlating the output signals of 1 and PD2 with the shift of the focus position. Specifically, assuming that the output signals from the respective portions of the pattern of the four-division photodiodes PD1 and PD2 shown in FIG. 5 are A _{1 to} A ₄ and B _{1 to} B ₄ , respectively, (A
_{1 + A 4 + B 2 +} B 3) - (A 2 + A 3 + B 1 + B 4)
To form a focus error signal. At this time, the zero point of this focus error signal corresponds to the point where the focus position coincides with the recording surface of the magneto-optical disk, that is, the just focus point, and feedback is provided to the focus servo system so that this focus error signal becomes zero. give. In this way, the just focus state is maintained.

On the other hand, the photodiodes PD1 and PD
Output signals A _{1 to} A ₄ and B from each part of the pattern 2
_{Using 1 to} B ₄ , (A ₃ + A ₄ + B ₁ + B ₂ ) − (A
₁ + A ₂ + B ₃ + B ₄ ) forms a tracking error signal. Then, feedback is given to the tracking servo system so that the tracking error signal becomes zero. In this way, the tracking is surely performed.

As described above, according to the laser coupler of the second embodiment, the photodiode PD1 has the first structure.
Since it has a comb-shaped electrode facing structure similar to the semiconductor light receiving element according to the embodiment of the present invention and has a polarization separation function and a polarization detection function, an anisotropic crystal or a polarization separation film is incorporated as a polarizer in a conventional laser coupler to generate light. Unlike the case of configuring a pickup, it is possible to simultaneously achieve a thin optical pickup and a low cost.

The embodiments of the present invention have been specifically described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, in the above-described first embodiment, the n-type semiconductor layer 2 is provided on the semi-insulating semiconductor substrate 1, but a p-type semiconductor layer is provided instead of the n-type semiconductor layer 2. The comb electrodes 3 and 4 may be provided on the p-type semiconductor layer.

Further, in the above-mentioned first embodiment,
Although the comb electrodes 3 and 4 are formed by the lift-off method, the comb electrodes 3 and 4 are formed on the entire surface of the n-type semiconductor layer 2 by a film of a metal such as Ti, Pt, or Al by a vacuum deposition method or the like. After forming the, it may be formed by patterning this by etching.

Further, although the four-division photodiodes PD1 and PD2 are used in the above-described second embodiment, the photodiodes PD1 and PD2 may be, for example, three-division photodiodes.

[0046]

As described above, according to the present invention, since the pair of comb-shaped electrodes constitutes the wire grid polarizer, this semiconductor light receiving element has a polarization separation function and a polarization detection function. . By using this semiconductor light receiving element in a reproducing optical pickup of a magneto-optical disk recording / reproducing apparatus, it is possible to simultaneously achieve a thin optical pickup and a low cost.

[Brief description of drawings]

FIG. 1 is a plan view showing a semiconductor light receiving element according to a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along line II-II of the semiconductor light receiving element shown in FIG.

FIG. 3 is a block diagram showing a state in which an amplifier circuit is connected to the semiconductor light receiving element according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a laser coupler according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram showing patterns of photodiodes PD1 and PD2 in a laser coupler according to a second embodiment of the present invention.

FIG. 6 is a schematic diagram showing an example of a specific structure of a photodiode PD1 in the laser coupler according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semi-insulating semiconductor substrate 2 n-type semiconductor layer 3, 4, 12, 13 Comb type electrode 5 Depletion layer 11 Photodiode IC 16 Micro prism 18 Semiconductor laser 19 Photodiode PD1, PD2 Photodiode

Claims (3)

[Claims] 1. A semiconductor photodetector having a structure in which a pair of comb-shaped electrodes are provided on a semiconductor substrate so as to face each other, wherein the pair of comb-shaped electrodes constitutes a wire grid polarizer. Semiconductor light receiving element. 2. The pair of comb electrodes are in Schottky contact with the semiconductor substrate.
The semiconductor light receiving element as described in the above. 3. The semiconductor substrate has a structure in which a semiconductor layer of one conductivity type is provided on a semi-insulating semiconductor substrate, and the pair of comb-shaped electrodes are in Schottky contact with the semiconductor layer. The semiconductor light receiving element according to claim 1, which is characterized in that.